A contact lens is a thin plastic or glass lens that is fitted over the cornea of the eye to correct vision defects. Various types of contact lenses exist that are designed to treat various types of vision defects. A phakic IOC lens is a lens that is implanted behind a person's cornea and works in conjunction with the natural crystalline lens of the eye to provide vision correction. Phakic IOC lenses are typically made of a material called polymethylmethacrylate (PMMA). The term “phakic” means that the eye with which the phakic IOC lens is used possesses the natural crystalline lens of the eye.
Typical lenses, including both contact lenses and phakic IOC lenses, are designed and manufactured to provide only the central portion of the lens with optical control. The central portion of the lens is deemed most important because it affects central vision, which is much more accurate than peripheral vision. The “central portion” of the lens, as that term is used herein, is intended to denote the portion of the lens that is optically controlled to provide an intended optical effect on a person's central vision. The central portion of a typical soft contact lens extends from the center of the lens outwardly to a distance of approximately 3.5 to 4 millimeters (mm) at the periphery of the central portion. This corresponds to a radial distance, r, that ranges from r=0.0 mm at the center of the lens to r≈3.5 or 4.0 mm at the boundary where the central and peripheral portions of the lens meet. The peripheral portion of a typical contact lens has a peripheral portion that starts where the central portion ends (e.g., at r≈3.5 or 4.0 mm) and extends outwardly a radial distance from the lens center of r≈7.0. Thus, the typical soft contact lens has a total diameter of approximately 14.0 mm.
It is believed that central vision is more accurate than peripheral vision due to the relatively high density of photoreceptors in and around the center of the retina of the eye. These photoreceptors, also known as “cones”, are responsible for daylight and color vision and are concentrated in a small depression near the center of the retina known as the fovea centralis. This dense concentration of cones provides this region of the retina with the greatest visual acuity. Acuity drops dramatically in the peripheral region of the retina. Central vision allows a person to distinguish smaller features that are near or at the center of the field of view, whereas features that are outside of the center of the field of view must be larger for the person to distinguish them through peripheral vision.
Soft contact lenses are not designed to provide optical control over the peripheral portions of the lenses because the peripheral portions do not affect the central vision of the eye. The light rays that pass through the peripheral portion of a typical soft contact lens are not focused in the central region of the retina, and thus do not affect the central vision of the eye. The peripheral portion of a typical soft contact lens sometimes includes a blending or transitioning portion that connects the central portion to the peripheral portion. This blending portion does not designed to provide optical control, and therefore does not provide vision correction except in cases where the pupils of the eye are small. The purpose of the blending portion is simply to connect the central and peripheral portions to each other.
Although an eye's corneal diameter typically ranges from about 11 mm to about 12 mm, the central portion of a typical soft contact lens typically ranges from about 7 mm to about 8 mm in diameter (i.e., r≈3.5 to 4 mm). The diameter of the central vision zone of the eye is generally defined as the region that provides central vision when the pupil is no larger than 7 mm in diameter under scotopic viewing conditions. The term “scotopic” means the ability to see in darkness or dim light, also referred to as dark-adapted vision. Although a typical soft contact lens is about 14 mm in total diameter, only the central 7 or 8 mm diameter portion provides vision correction. The peripheral portion, also commonly referred to as the lenticular portion, serves to stabilize the lens and fit the lens comfortably over the limbus of the eye.
While the peripheral portion of a typical soft contact lens is not designed to provide optical control over light entering the eye, it has been suggested that peripheral vision images may have important effects on the vision system of the eye. For example, it has been suggested that vision in the peripheral range drives myopia. Myopia is the medical term for nearsightedness. People with myopia see objects that are closer to the eye more clearly, while distant objects appear blurred or fuzzy.
The manner in which peripheral vision may affect the vision system of the eye is explained in, for example, U.S. Pat. No. 7,025,460 to Smith, et al. Specifically, in Column 3, lines 42-47 of Smith et al. states:                “The present invention is based on new learning from our experiments that demonstrates that the peripheral retinal image (i.e. peripheral vision) plays a major role in determining overall eye length, and is an effective stimulus that promotes peripheral and total eye growth that results in axial elongation, an overall increase in eye size and myopia.”        
Smith et al. discloses various methods and devices for providing a visual image that has “a peripheral field image location that is positioned more anteriorly to (or in front of) the peripheral retina (i.e. toward the cornea or the front of the eye) than normally in the uncorrected condition, while the central field image location is positioned near the central retina (i.e. the fovea)”. Smith et al. discloses that this arrangement minimizes or eliminates the stimulus for eye axial elongation leading to myopia.
U.S. Pat. No. 6,045,578 to Collins et al. discloses a method for treating myopia that uses a lens having a central portion (i.e., an optic zone) that causes paraxial light rays entering the center region of the central portion of the lens to be focused on the retina while causing light rays entering the peripheral region of the central portion of the lens to be focused in a plane between the cornea and the retina, thereby producing positive spherical aberration of the image on the retina. Collins et al. states that this positive spherical aberration has a physiological effect on the eye that tends to inhibit growth of the eye, thus mitigating the tendency of the myopic eye to grow longer.
Collins et al. also discloses an embodiment for mitigating hyperopia by using a lens having a central portion (i.e., an optic zone) that causes paraxial light rays entering the center region of the central portion of the lens to be focused on the retina while causing light rays entering the peripheral region of the central portion of the lens to be focused in a plane behind the retina, thereby producing negative spherical aberration of the image on the retina. Collins et al. states that this negative spherical aberration has a physiological effect on the eye that tends to enhance growth of the eye, thus mitigating hyperopia.
While Smith et al. and Collins et al. both recognize the importance of the peripheral vision image, these patents are directed to the effects that light rays passing through the periphery of the central portion of the lens have on the vision system of the eye. In other words, these patents are not directed to the effects that light rays passing through the peripheral portion of the lens (i.e., the portion outside the approximately 7 or 8 mm diameter central portion of the lens) have on the eye. Therefore, the effects that these light rays produce on the vision system are limited by the ability of the central portion of the lens to provide the necessary optical control.
For a variety of reasons, including those described in Smith et al. and Collins et al., it would be desirable to provide a lens having a peripheral portion that provides optical control. However, because the peripheral portion of the lens is used to stabilize the lens and to fit the lens to the surface of the eyeball, and is normally the same for every lens of a given lens series, the peripheral portion is normally not designed to provide optical control. If the peripheral portion were to be designed to provide optical control, it could not be kept the same for an entire lens series. Rather, the peripheral portion would need to be varied from lens to lens in order to ensure that the optical control it provides works with the optical control provided by the central portion. Consequently, the traditional view in the soft contact lens industry is that because central vision is most important, and because providing the peripheral portion of the lens with optical control would require that different lenses of the same series be manufactured with different peripheral portions, it is undesirable to design contact lenses to have peripheral portions that provide optical control.
Furthermore, increasing the diameter of the optical zone of a contact lens presents certain problems that would need to be solved by the contact lens industry. For example, for a typical lens series comprising lenses ranging in optical power from −10 D to +6 D and having 8 mm diameter central portions, the sagittal depth (SAG) difference for different lenses of the series is roughly 20 micrometers (μm) per Diopter. Therefore, both the thickness of the lens at the center of the central portion and at the edge of the central portion vary over a lens series. If the diameter of the central portion were to be increased, the SAG difference across the series would increase to an even greater extent. Because the front surface of the peripheral portion is generally constant across the power range of the series, increasing the diameter of the central portion would require that the slope and curvature of the blending portion be varied to an even greater extent from lens to lens across a given series. This presents even greater difficulties in terms of lens design and manufacture.
Accordingly, a need exists for a contact lens having a peripheral portion that provides optical control and that can be easily designed and manufactured.